1. Field of the Invention
The present invention relates to a mobile computer device capable of carrying out communications while moving among a plurality of inter-connected networks, and a mobile computer management device for managing a moving location information of the mobile computer and transferring packets destined to the mobile computer to a current location of the mobile computer, as well as a mobile computer management method and a communication control method suitable for these devices.
2. Description of the Background Art
In conjunction with availability of a computer system in smaller size and lower cost and a more enriched network environment, the use of computer system has been rapidly expanded into variety of fields, and there is also a transition from a centralized system to a distributed system. In this regard, in recent years, because of the advance and spread of the computer network technology in addition to the progress and improved performance of the computer system itself, it has become possible to realize not only a sharing of resources such as files and printers within an office but also communications (electronic mail, electronic news, file transfer etc.) with outside of an office or organization, and these communications are now widely used.
In particular, in recent years, the use of the world's largest computer network called “Internet” has become very popular, and there are new computer businesses for connecting to the Internet and utilizing open information and services, or for providing information and services to external users who make accesses through the Internet. In addition, new technology is developed in relation to the use of the Internet.
Also, in conjunction with the spread of such networks, there are technological developments regarding the mobile computing. In the mobile computing, a user carries along a portable computer terminal and makes communications while moving over networks. In some cases, the user may change a location on a network while continuing the communication, so that there is a need for a scheme that manages a changing address of a mobile computer on a network during such a communication in order to route the communication content correctly.
In general, in a case of realizing the mobile computing, a router (home agent) for managing the visiting site information of the mobile computer is provided at a network (home network) to which the mobile computer belongs, and when the mobile computer is away from the home network, the mobile computer sends a registration message for indicating a current location to this home agent. When this registration message is received, the transmission of data destined to the mobile computer is realized by capturing it by the home agent of the mobile computer, and carrying out the data routing control with respect to the mobile computer by encapsulating an IP packet destined to an original address of the mobile computer within a packet destined to a current location address of the mobile computer.
For example, in FIG. 1, this role is played by a home agent (HA) 5 in a case where the mobile computer 2 that originally belongs to the home network 1a moves to another network 1b and carries out the communication with another computer (correspondent host: CH) 3 within the other network 1c. This is a scheme called Mobile IP which is currently in a process of being standardized by the mobile-IP working group of the IETF which is the standardizing organization for the Internet (see, IETF RFC 2002, IP mobility support (C. Perkins)).
Now, in the Mobile IP scheme, the mobile transparency of the mobile computer on the IP networks is supported by continually using a fixed address assigned at a network (home network) to which the mobile computer originally belongs even at visited sites. This address will be referred to as a home address. When the mobile computer moves to a new visited site, the mobile computer sends a current location registration message as shown in FIG. 2 to the home agent, according to the specification of RFC 2002. In FIG. 2, “Home Address” is the home address of the mobile computer, “Care-of Address” is a temporal address for receiving packets transferred from the home agent at the visited site network, which is to be used as a destination address to be attached to an outer header of (encapsulated) data to be transferred from the home agent.
Namely, in order to carry out communications according to the Mobile IP of RFC 2002, two addresses of (1) a fixed home address of the home network, and (2) a Care-of address allocated at the visited site network, are necessary.
On the other hand, as far as the address management scheme at the home network is concerned, it was common to allocate addresses fixedly to PCs or workstations provided at the home network, but due to the spread of portable PCs and also in order to simplify the address management, it is now rather normal to allocate addresses dynamically to hosts using a method called DHCP (Dynamic Host Configuration Protocol) (see RFC 1541 and 2131).
In the DHCP, IP addresses are dynamically allocated by a DHCP server in response to a request from each host, from a certain address region that is reserved in advance.
If the home site of the mobile computer which moves while using the Mobile IP is operated by this DHCP, there is no guarantee for being capable of acquiring a specific IP address again when the mobile computer is re-connected at the visited site or the mobile computer moves to another subnet. Also, there can be cases where, after the mobile computer moves, another host uses an IP address that has been used by the mobile computer up until then, so that it is difficult to use the address allocated by the DHCP as a home address of the Mobile IP according to the conventional specification of RFC 2002 alone.
Thus in the conventional Mobile IP scheme, if the home network of the mobile computer is operated by the dynamic address allocation such as DHCP, there is a difficulty when the mobile computer tries to re-connect after moving to the visited site, in that there is no guarantee for continually using an address that has been allocated at the home site up until then. In particular, in the case of carrying out home address dependent communication processing at the visited site, such communications become impossible when the home address is changed.